The present invention relates to a method of determining exposures in printing.
In making positive prints on photographic paper from originals such as negatives, positives or the like, it is usual to determine the exposure in accordance with the average density over the whole area of the original to be printed.
Generally, originals include a background image besides the image of a principal subject matter (which is referred to hereinafter as the principal subject image) intended to be photographed. In the above exposure determination, the density measurement is conducted over the whole area of the original to be printed, namely, effected independently of the principal subject image thereof, with the result that the obtained prints are not always satisfactory because the principal subject image is printed with improper density.
In color printing, as is well known in the art, the determination of exposure is based on the large area transmittance densities of red, green and blue of the color original to be printed, and the proportions of the three primary color components of printing light are controlled.
In order to solve the above-described problem, a printing method has been proposed in, for example, Japanese Patent Publ. No. 55-29412 wherein an original is divided into a plurality of image sections, one of them being selected as the principal subject image. The selected image section is scanned to measure its densities at a number of points (each of which represents a picture element) thereof in order to calculate at least one characteristic value of density from the measured densities. On the basis of the characteristic density value and the average density over the whole area of the original, the printing exposure is determined. In this printing method, however, it is hard to control exposures with a high accuracy, since there is given no useful information for obtaining prints of proper tint both as to the characteristic density value of the principal image and as to the average density over the whole area of the original image: because of the inclusion of the principal subject image in the whole area of the original image, the information as to density cannot distingush between the densities of the principal subject image and its background image.
In conventional printing methods including the above-described one, the average density of the whole area of the originals is in fact used to obtain prints of proper tint. On the other hand, the empirical rule that the openair subject matter of originals generally has a color close to gray is applicable to the background image thereof. But if the principal subject image of the originals has an intended tint, the empirical rule will be often inapplicable.